really nice, especially the last level. as a very cautious player i never really attacked with a large force, only one or two ships at a time (the ones that cost 450 and 500, forgot their names) while upgrading everything to max level. then i saved up some money untill i had like 10.000 and attacked - well, more like tried to attack - with full force. unfortunately the enemy died before i even had a chance to fully launch the final attack. last level was where i finally could attack with full force and even had to actually care for not dieing while attacking, especially in the second phase.
@Siruss: had the same thing multiple times, but you just have to refresh the page and then you can continue normally untill it happens again. fortunately it seems to only happen at the start of the level and in the research menu, so none of your progress will be lost. ;)